Today, there exist mainly three types of water heating systems for table-top coffee makers, tea makers, beverage vending machine and the like. A first type is a boiler. A heater such as an electrical resistant coil is immersed inside a water tank and in direct contact with the water. Hot water is prepared and stored continuously. A second type is a thermoblock system. A heating element and a water tube are cast inside an aluminum block, which is kept at a high temperature as long as the machine is maintained in the use mode. Water flowing through the water tube is heated by the stored heat of the aluminum block. A third type is a heating belt. A heating unit surrounds a water tank and heats the wall of the water tank, thus heating the water inside.
All of the above-described heating systems cannot provide hot water on-demand, since they cannot heat water without delay. A certain preparation time is necessary. These systems are relatively bulky and heavy.
Therefore, a fourth type of water heating system is a continuous flow heater using a tube heating water as water circulates continuously inside the tube. In particular, WO 2008/110847 A2 shows a continuous-flow water heating apparatus, which comprises a heating element, which is arranged within a water tube. The water tube and the heating element form a gap through which the water flows. This continuous flow heating system has disadvantages though, since a very long water tube and therefore also a very long heating element is necessary for heating the water and since the time of exposure to the heat of the heating element is very short due to the geometry of the water tube. This results in a high weight and a high volume of the resulting water heater.
U.S. Pat. No. 4,975,559 relates to a device for heating and aerating water in a coffee machine. The water circuit has water circulation channels and air retaining pockets disposed at intervals along the water circulation channels above the normal water levels of the channels. The air retaining pockets provide turbulence in circulating water and cause the air retained in the pockets to be dissolved in the water.
US2006027103A1 relates to a device for heating liquid in a beverage machine. The device comprises a tube heater with a water inlet, a water outlet and an insert inside the tube comprising helical grooves. The water is forced through a small gap in helical manner. One problem is that water temperature is difficult to control and can be over-heated. This requires a complex set of resistors which are electrically linked. Furthermore, the inside insert provides an elevated pressure loss in the fluid circuit that needs to be overcome.